This application is based on application No. 2000-290545 filed in Japan, the content of which is hereby incorporated by reference.
The present invention relates to a zoom optical system, and more specifically, to a finite-distance zoom optical system suitable particularly as an imaging optical system for a film scanner or the like.
Conventionally, apparatuses such as film scanners that scan images on various sizes of photographic films and capture the images as image information have had a predetermined structure in order that different film formats can be handled. That is, in these apparatuses, films are scanned while the imaging magnification is varied according to the film format by use of a finite-distance zoom optical system with a fixed conjugate distance.
However, in this structure, when a film position error is corrected in focusing or the like, the captured area of the film image formed on the image sensing device changes due to the change in the magnification of the optical system.
An object of the present invention is to provide an improved zoom optical system.
Another object of the present invention is to provide a finite-distance zoom optical system having a system that is capable of performing imaging at a required magnification by eliminating the magnification change due to the conjugate distance change caused by a film position error or the like.
The above-mentioned object is attained by a zoom optical system comprising: a focus adjusting unit that performs focusing for an object; and a magnification adjusting unit that corrects a change in optical magnification caused by the focusing.